The letter from Lord Nash, the Schools Minister, raises concerns that just 32 per cent of pupils gained good GCSEs last summer, down from 35 per cent a year earlier and below the Government's minimum threshold of 40 per cent.

At the same time, the school was judged to be "inadequate" by Ofsted following an inspection at the end of last year, with the watchdog concluding that teaching was poor, marking and planning of work was inadequate, expectations were too low, pupils had a bad attitude in lessons and the expulsion rate was too high.

The school was opened in 2009 – replacing a community comprehensive on the site.

It had been rated as "good" by inspectors in July 2012 but this was downgraded following another probe last November.

Prof Alan Ford, pro-vice-chancellor for teaching and learning at Nottingham University, which is a member of the elite Russell Group, said: “As soon as it became clear that this year's GCSE results were not where they should be, we put a plan of action in place to improve teaching and learning, strengthen management and leadership, and improve results for pupils at NUSA.

"This represents a new phase for NUSA. It will mean a focus on improving learning outcomes for the school, strengthening leadership and providing the right environment for pupils to succeed."

The school said it was teaming up with the Torch Academy Gateway Trust in an attempt to raise standards.

A pre-warning letter gives schools two weeks to come up with an action plan before being issued with a formal warning notice. This can lead to the Government appointing additional directors and – ultimately – replacing the sponsor altogether.